1. Field of the Invention
This invention is in the field of amplifier protection circuits and more particularly to protection circuits for amplifiers having an inductive load and having current sensing feedback circuits.
2. Description of the Prior Art
Deflection amplifiers used for deflection yoke coils in stroke written cathode ray tubes are subject to dissipation of very large amounts of power in their output transistors under certain operating conditions. The coil is used to cause movement of an electron beam across the tube screen. Substantially high coil currents accompany high speed movement of the beam and may also accompany low speed movement or beam hold condition distant from screen center. Substantially high supply voltages and power are required to cause rapid changes in current in the inductive yoke coil for the high speed beam movement. During low speed beam movement or beam hold condition at an appreciable distance from screen center, as are typical in the operation of stroke written cathode ray tubes, only a small portion of the high supply voltage appears across the yoke coil although current through the yoke coil remains high. The power difference between the substantial supply power and the low power dissipated in the low resistance yoke coil during low speed beam movement or beam hold condition is dissipated in the amplifier output transistors. Since the total resistance of the inductive load and associated current sensing resistor may be in the order of only one ohm, very large power dissipation occurs in the amplifier output transistors during low speed beam movement or beam hold condition. The transistors often dissipate hundreds of watts during this condition. As a result large expensive output transistors and large bulky heat sinks are required to prevent transistor damage.